This invention relates to the detection of angular rate and more particularly to an open loop laser gyro.
In general, laser gyros operate by arranging a laser to inject counter-propagating beams of light into a ring resonator. If the frequency of the injected light is such that an integral number of wavelengths fit within the ring resonator, the ring will be in resonance. When the ring has an angular velocity, the apparent path length for radiation traveling in the direction of rotation will be longer than that for radiation traveling in the opposite direction. The change in apparent path length will disturb the resonance condition. The resonance condition can be re-established by altering the frequency of light injected into the ring. The frequency change needed to re-establish resonance is then a measure of the angular rate of the ring.
In closed loop laser gyros, the frequency of the light injected into the ring is altered, often using acousto-optic frequency shifters, to maintain the ring on resonance. These gyros are closed loop in the sense that the injected frequency is varied so as to maintain the resonator on resonance during ring rotation. One such known closed loop laser gyro is disclosed in U.S. Pat. No. 4,326,803. In addition to the laser and the ring resonator, this gyro requires a pair of frequency shifters for its operation, which adds to its cost and complexity.
It is an object of this invention to provide an open loop laser gyro which eliminates the need for frequency shifters.
It is a further object of the invention to provide a thin film laser gyroscope which is simpler and substantially less costly than those known in the prior art.
Yet another object of the invention is a laser gyroscope which can be implemented utilizing thin film technology.